Flash lamps



Sept 2, 1965 EIZO GOTO ETAL FLASH LAMPS Filed Jan. 23, 1963 Time (mi/isecond 2' 3 [n farna/ res/'slance of ce/lLQ) 0 wwwz Agbumm s Emma Q EB QQE uumt Q mxibmt m United States Patent 3,208,246 FLASH LAMPS Eizo Goto, Chigasaki-shi, Namio Iwata, Odawara-shi, and Koichi Talrahashi, Tokyo, Japan, assignors to Tokyo Shibaura Electric (30., Ltd, Horikawacho, Kawasakishi, Japan, a corporation of Japan Filed Jan. 23, 1963, Ser. No. 253,413 Claims priority, application Japan, Jan. 23, 1962, 37/ 1,735 2 Claims. (Cl. 67-31) The present invention relates to improvements in or relating to flash lamps.

Flash lamps in general include a glass bulb filled with a combustion-accelerating gas such as oxygen and accommodating a mass of finely shredded foil of metallic lightproducing material such as aluminum or zirconium with a heating. element in the form of a high-melting metal filament, for example, of tungsten mounted across the ends of two lead-in wires sealed in the bulb. The heating element is coated with a readily combustible igniting material. When the filament is heated to intense heat by a current supply through the lead-in wires, the igniting material on the filament is fired by the heat and thus itself rapidly produces heat sufiicient to ignite the lightproducing material so that the latter aided by the combustion-accelerating gas filled in the bulb is burnt to produce light in a desired limited time period. The coating of igniting material is generally formed first by immersing the ends of the lead-in wires carrying the heating element into a pasty liquid including a mixture of magnesium, zirconium and potassium chlorate each in powder form and a solution of an organic binder such as nitrocellulose to coat the heating element with the paste, and then drying the coated paste. The coating of igniting material tends to fall off when subjected to heat in the lamp assembling stage. This tendency increases with reduction in size of the lamps and thus reduces the yield of lamp production. Also, it is very difiicult to control the quantity and composition of the paste coated to a definite level, and this forms an important factor causing variation in the lightemitting characteristics of the lamps. Further, the igniting material including a readily combustible substance such as zirconium and an oxidizer such as potassium chlorate involves the danger of explosion, calling for particular attention to the handling of the igniting material and the lamp assembling operation.

The present invention has for its object to provide a highly improved flash lamp which is provided with a novel igniting mechanism in place of the conventional structure including a heating element coated with igniting material and thus not only is entirely free from the above difficulties previously met but has a number of further advantages as described hereinafter.

According to the present invention, there is provided a flash lamp including a glass bulb and two lead-in wires extending through the wall of the glass bulb, said bulb containing a combustion-accelerating gas filling at a pressure not lower than the atmospheric pressure, a mass of finely shredded foil of a readily combustible light-producing material selected from the group consisting of metals such as zirconium, titanium, and tantalum and alloys containing any of said metals as a main ingredient and enclosed in the glass bulb, and an igniting element free from igniting paste in the form of a filament mounted across the inner ends of the two lead-in wires, said filament being also formed of any material selected from said group. The flash lamp is thus seen to be primerless.

The foregoing and other objects, features and advantages will become apparent from the following description when taken with reference to the accompanying drawings, which illustrate one preferred embodiment of the invention and in which:

FIG. 1 is a partly cutaway side elevation of a flash lamp embodying the present invention; and

FIGS. 2 and 3 graphically illustrate the light-producing characteristics of the inventive lamp in comparison with those of conventional flash lamps.

In FIG. 1, the flash lamp illustrated includes a glass bulb 1 having an interior volume of approximately 1.2 cubic centimeters and enclosing approximately 21 milligrams of light-producing material in the form of a mass of finely shredded foil 2 of zirconium having a cross section of approximately 28 4 x 55 .4. The glass bulb is filled with oxygen as a combustion-accelerating gas at a pressure of approximately 3500 mm. Hg. Two lead-in wires 3 are sealed in the stem portion of the glass bulb and together carry an igniting element 4 in the form of a zirconium filament secured at opposite ends to the respective inner ends of the lead-in wires 3 and thus embedded in the mass of light-producing foil. The igniting filamenthas a crosssectional area of approximately 0.0004 mm. and a length of about 1.5 mm. With lamps of such structure, it has been found that the light-producing material 2 violently burns to produce light in an extremely short period of time when an electric current from a series connection of two small dry cells having a rated electromotive force of 1.5 volts is passed through the igniting element by way of the lead-in wires 3. It is supposed that the igniting element thus energized to heat reacts with the atmosphere of combustion-accelerating gas thereby to be suddenly further heated to fuse and explosively scattered so that the lightproducing material is ignited to violently burn by the aid of the combustion-accelerating gas. While with conventional lamps the light-producing material has been ignited to burn through the medium of the firing of the igniting material caused by a heating element, the light-producing material in the lamp according to the present invention is ignited to burn immediately through the heat generation of the igniting element itself. Thus, according to the present invention, the difliculties previously met in the art are completely overcome giving lamp performances highly improved over those of conventional flash lamps, as will 7 be described below in detail.

Firstly, according to the present invention, the production of flash lamps is easy, safe and high in yield since no dangerous, highly exfoliative igniting material is employed.

Secondly, the igniting element taking the form of a metallic filament can be prepared with a high degree of uniformity to give lamps light-producing characteristics of highly improved uniformity. For example, it has been found that the range of variation in length of time between the time of energization of the lamp and the peak of light flux produced is reduced to about one-third of that with conventional flash lamps.

Thirdly, the blackening of the glass wall of the lamp is diminished to increase the amount of available luminus flux by approximately 20% or more. The reason for thisis presumably as follows. With conventional lamps, when fired the igniting material has scattered to reachthe vicin-.

ity of the wall of the glass bulb igniting the light-producing material so as to cause blackening of the glass wall in the cour'seof combustion of the light-producing material. On the other hand, with the inventive lamp, the range of scattering of the igniting element is rather limited and the light producing material starts to burn largely in the vicinity of the bulb center so that the blackening of the bulb wall is effectively prevented. Also, the color temperature of the light produced with the inventive lamp is raised by approximately 250 K. compared to that of 3 conventional ones. This is particularly advantageous for example in color photography.

Fourthly, use of the lamp according to the present invention extends the effective life of service of the battery serving as a power source for burning the lamp to a substantial extent. While, with conventional lamps, the igniting material has been heated indirectly by the heating element, the igniting element in the lamp of the present invention is itself heated by the electric current passing therethrough and hence with a highly improved heating efliciency, thus minimizing the amount of energy required to light the lamp to approximately 1.2 to 1.5 Joules as compared to approximately 3 to 4 10- Joules with conventional flash lamps. Because of this, satisfactory light-producing characteristics can now be obtained even where a limited current is employed.

Fifthly, with conventional lamps, which have included a heater filament taking the form of a very fine metallic wire having a diameter for example of about to p. for the purpose of obtaining satisfactory characteristics with the light-producing material, it has frequently occurred that the filament is fused to break after the energization of the lamp and before the firing of the igniting material, causing misfiring of the lamp. On the other hand, according to the present invention, there is substantially no danger of such misfiring since the light-producing material is ignited by heat generated by the igniting element itself.

Finally, according to the present invention, there is no danger of the lamp being accidentally burnt or exploded under the influence of a high-frequency electromagnetic field. With conventional flash lamps, the heating element must be heated to a considerably high temperature to fire the igniting material. However, the igniting material, which contains an oxidizing agent in itself, is readily fired at relatively low temperatures. Therefore, if the lamp is placed in a high-frequency electromagnetic field, the electric current induced therein may heat the igniting material to cause an unwanted firing thereof. On the other hand, the igniting element in the lamp of the present invention is much more stable and safer as it acts to ignite only after it has attained a temperature much higher than with the case of any conventional igniting material.

The following are the results of performance tests conducted with lamps constructed according to the present invention and conventional lamps having the same interior volume of the glass bulb and the same amount of zirconium as a light-producing material.

FIG. 2 graphically illustrates the relationship between the luminous flux and the time elapse after the lamp is switched on. The abscissa represents the time in milliseconds and the ordinate the luminous flux in lumens. The solid-line and broken-line curves correspond to the inventive and conventional lamps, respectively.

FIG. 3 is a graphical representation of the relationship between the internal resistance of the battery as a power source for burning the lamp (said resistance increasing as the battery deteriorates) and the length of time between the switching-on of the lamp and the peak of the luminous flux produced. The abscissa represents 43- the resistance in ohms, Q, and the ordinate the time length in milliseconds. The solid-line and broken-line curves correspond to the inventive and conventional lamps, respectively.

As apparent from the foregoing, the lamp according to the present invention has many advantageous features including improved light-producing characteristics. In connection with this, it is first noted that a metal or material selected from the group consisting of zirconium, titanium, tantalum or an alloy containing as a main ingredient any such metal can be employed in the igniting element or as the light-producing material with the same effect as zirconium.

Secondly, the igniting element is required to have a surface clean enough to readily react with the combustionaccelerating gas.

Thirdly, the combustion-accelerating gas is filled in the bulb desirably at a pressure equal to or higher than the atmospheric pressure. With lower pressures, particularly where the lamp is small in size, its light-producing characteristics would be impaired.

Finally, the characteristics of the light-producing material including the igniting time and the length of burning period can be controlled, for example, by varying the thickness of the light-producing material. The range of control can be substantially extended without impairing the light-producing characteristics of the lamp to any substantial extent by admixing an appropriate quantity of rare gas such as argon, neon or xenon to the combustion-accelerating gas.

It is to be understood that the present invention is not to be limited to the details set forth but is to be accorded the full scope of the appended claims.

What is claimed is:

1. A primerless flash lamp comprising a glass bulb, lead-in wires extending through the wall of the glass bulb, a combustion-accelerating gas filling of oxygen contained in the glass bulb at a pressure of approximately 3500 mm. Hg, a mass of finely shredded foil of a readily combustible light-producing material selected from the group consisting of zirconium, titanium and tantalum and alloys containing any of the materials as a main ingredient and enclosed in the glass bulb, and an igniting filament mounted across the lead-in wires adjacent their inner ends, said filament being of a material selected from said group.

2. A flash lamp comprising a glass bulb and lead-in wires extending through the wall of the glass bulb, said bulb containing a combustion-accelerating gas filling at a pressure not lower than the atmospheric pressure, a mass of finely shredded foil of zirconium within the bulb, and an igniting element free from igniting paste comprising a filament mounted across the lead-in wires within the bulb, said filament being of a material selected from the group consisting of zirconium, titanium and tantalum.

References Cited by the Examiner UNITED STATES PATENTS 2,013,371 9/35 Van Liempt et a1 a- 67-31 2,571,799 10/51 Van Uden et al. 67-31 2,865,186 12/58 Anderson et al. 6731 2,982,119 5/61 Anderson 67-31 3,045,460 7/62 Brouse et al. 6731 FOREIGN PATENTS 588,183 12/59 Canada.

FREDERICK L. MATTESON, IR., Primary Examiner.

EDWARD J. MICHAEL, Examiner. 

1. A PRIMERLESS FLASH LAMP COMPRISING A GLASS BULB, LEAD-IN WIRES EXTENDING THROUGH THE WALL OF THE GLASS BULB, A COMBUSTION-ACCELERATING GAS FILLING OF OXYGEN CONTAINED IN THE GLASS BULB AT A PRESSURE OF APPROXIMATELY 3500 MM. HG, A MASS OF FINELY SHREDDED FOIL OF A READILY COMBUSTIBLE LIGHT-PRODUCING MATERIAL SELECTED FROM THE GROUP CONSISTING OF ZIROCNIUM, TITANIUM AND TANTALUM AND ALLOYS CONTAINING ANY OF THE MATERIALS AS A MAIN INGREDIENT AND ENCLOSED IN THE GLASS BULB, AND AN IGNITING FILAMENT MOUNTED ACROSS THE LEAD-IN WIRES ADJACENT THEIR INNER ENDS, SAID FILAMENT BEING OF A MATERIAL SELECTED FROM SAID GROUP. 